This invention relates to A.C. power control circuitry and more particularly to a timer for driving a load such as a transformer for use in welding apparatus.
In resistance welding circuitry, a transformer is typically used to energize the welder electrodes. Prior art weld timer circuits for controlling the power supplied to the transformer have required the use of tubes, usually hydrogen thyratrons. Similar circuitry has been common in other areas where it is desired to control the delivery of large amounts of power for dissipation by a load.
Such circuitry has proved far from satisfactory. The thyratron tubes are extremely expensive, require long warm-up periods and waste large amounts of power in stand-by condition. In particular, the resultant weld timers have been heavy, bulky, expensive and unreliable.